1. Field of the Invention
The present invention relates generally to a fluid-filled type vibration damping device that utilizes vibration damping effect on the basis of the flow action of the fluid filling a fluid chamber. More particularly, the present invention pertains to a fluid-filled type active vibration damping device capable of exhibiting active vibration damping effect by exerting the oscillation force on a fluid chamber by means of an actuator.
2. Description of the Related Art
There have been known fluid-filled type vibration damping devices including a fluid chamber filled with a non-compressible fluid and capable of attaining vibration damping effect by utilizing flow behavior of the fluid induced during input of vibration. The fluid-filled type vibration damping device has a construction wherein a first mounting member and a second mounting member are elastically connected by a main rubber elastic body, and the main rubber elastic body partially defines a wall of the fluid chamber, in order to apply vibration to the fluid chamber. Also, in recent years, with the aim of realizing more enhanced vibration damping characteristics, proposed is an active type fluid-filled vibration damping device furnished with an electromagnetic or other actuator and able to actively control pressure in the fluid chamber (see Japanese Unexamined Patent Publication No. JP-A-2007-252017).
The fluid-filled type active vibration damping device as disclosed in Japanese Unexamined Patent Publication No. JP-A-2007-252017 includes an oscillation member that partially defines a wall of the fluid chamber, and the oscillation member is connected to an output shaft that is secured to a movable member of the actuator. With this arrangement, the oscillation force of the actuator is adapted to be exerted on the oscillation member via the output shaft. The oscillation member and the output shaft are interconnected at one point in the following way, for example. The oscillation member has a round tubular shape with a bottom and includes a swage hole that perforates its diametrical center section, while the output shaft includes a swage projection that projects on the center axis of the output shaft. The swage projection of the output shaft is inserted into the swage hole of the oscillation member, and then the upper end portion of the swage projection undergoes diameter expansion deformation so as to be secured by swaging to the rim of the opening of the swage hole.
However, since the connected section of the oscillation member and the output shaft is subjected to oscillations repeatedly from the actuator, more enhanced securing force may be required with the aim of obtaining durability over an extended period. In such cases, whereas the securing force in the vertical direction is obviously required, the securing force in the rotational direction may be appreciably required in order to avoid relative rotation of the oscillation member and the output shaft. Specifically, the connecting structure in which the oscillation member and the output shaft are interconnected only at one point in the diametrical center retains a relatively small securing force in the rotational direction. Therefore, especially in a case where smoothness of the superposed faces of the oscillation member and the output shaft is high and the securing force in the rotational direction based on the frictional force is small or the like, obtaining a large securing force in the rotational direction without complicating the structure has been required.